Growth hormone insensitivity syndrome occurs when the actions of pituitary growth hormone (GH) are chronically attenuated. Isolated GH insensitivity most commonly results from either loss of function mutations in the GH receptor or from high levels of circulating antibodies that neutralize GH. In the complete form of the syndrome, patients manifest extreme growth failure, decreased lean body mass, and metabolic abnormalities such as hypoglycemia. The disorder is very rare, and there is no commercial agent available that will effectively treat the condition.